Seven faces of a killer: Mass murderers

To mark the 150th anniversary of Berkshire's Broadmoor Hospital, a psychiatric unit for the criminally insane, we're looking at the psychology of some of the world's most dangerous killers. Each week criminologist Professor David Wilson will take a look at one of the seven typologies of a killer to explain why some people become murderers.

After last Monday's killing rampage at the US Naval Sea Systems Command headquarters in Washington DC, we look at spree and mass killers, and the motivations behind their crimes.

Watch Dr Wilson explain what makes a missionary killer

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